1. Field of the Invention
This invention relates to the joining together of tubing of dissimilar materials in a leakproof connection, and more particularly to the joining of a thermoplastic tube and a metallic tube.
2. Description of the Prior Art
Tubing of both a non-metallic and a metallic material is used as a conduit for gaseous or liquid fluids in aircraft as well as for other purposes. There are various characteristics of these different materials which make any one of them more adaptable or suitable for certain uses. For example, metallic tubing can withstand higher pressures. On the other hand, nonmetallic tubing is more flexible. If it is desired to use both a metallic and a nonmetallic tube, the joining of them together presents problems due to a difference in physical properties. In the instance here involving a fluidic/pneumatic control system for a helicopter cargo hook, polyethylene tubing is used for air conduction since it can be easily fabricated into the desired shape at low cost and weight. However, there are no known bonding agents or sealers that will adhere to polyethylene to provide the leakproof connections required in such a system.
In the prior art, Wolfe U.S. Pat. No. 3,476,408 and Farman U.S. Pat. No. 3,524,661 are directed to the problem of joining metallic pipes to thermoplastic pipes such as those made of polyethylene, Wolfe disclosing bonding means for the connection and Farman disclosing clamping means. Grenell U.S. Pat. No. 2,903,763 is directed to the joining of dissimilar metallic tubing by casting a metallic fitting sleeve around the ends of the tubing. In addition, Wallace U.S. Pat. No. 2,411,398 and Aschinger U.S. Pat. No. 3,033,919 show a molded connection in which material extends through perforations to provide an interlocking structure.